Ribbon surface for surface tangency

[magneplanar]

Has anyone used the ribbon surface feature generated from sketched curves?

I was playing around with it and I am not sure if it improves the surface tangency enough to be valuable. If one curve meets another curve that is circular in a "T" fashion then the ribbon surface seems to stick out beyond the second curve. I also tried doing this with just an extruded surface, on the same curve, without going all the way to the next perpendicular curve.

I am working on a motorcycle helmet and the top surface seems to connect better, but still some irregularities show in the curve analysis.

thanks in advance for whatever comments you provide...

cheers...

M

 

[jeff4136]

A Datum Ribbon can be created and used as a tangent direction
reference where no other references (tangent or normal) exist.


"not sure if it ~improves~ " makes me wonder what the expectations
are. I'm failing to visualize what you describe. Maybe post a
pic or example model with a little more explanation?

 

[magneplanar]

Jeff4136,

some images:

I may be doing this all wrong by trying to make such a large capping surface for the top of the helmet. The curve analysis shows a peak across the center and uneven matching with the side surfaces. I would like that to be better. If I do not have the ribbon then the surface moves inward like it was pushed in, tangent to a plane. The top ribbon seems like it is extruded left to right and does not follow the edge line . -The datum curves are hidden.
-The sides are not a revolved feature.
-The shape is altered to be more angular in the back.View attachment 3203
View attachment 3204

 

[jeff4136]

Ok, I see. You might try increasing the constraint influence value
to get that 'peak' out of the curvature graph. Also, fwiw, you should
get the same effect constraining the surface normal to the section curve
plane or tangent to an extruded surface. I think the neat thing about
Ribbons is the input curve sets you can use to create them. Normally,
tho, I'd use one of the other two constraint methods for the dome.


(And ...
If it were me; I'd go about that in a different way and avoid creating
the dome surface with singularities (where all the iso lines converge)
on the ends. What does an Offset analysis look like on what you've got?
If it looks good or you don't really care and you can get what you want;
proceed on. What I would probably do, tho, is create a four sided surface
and trim it to duplicate what you have (two sided) and then blend the side
surface between the trim edge and a curve on the bottom end. Might be
worth trying ...)

 

[magneplanar]

Jeff4136,

thanks for the tips, I tried expanding the width of the ribbon, it did not seem to improve substantiially. I do agree that the singularities are not acceptable, so I will see about rebuilding a more controlled surface as you described.

cheers...

M

 

[jeff4136]

I don't believe the Ribbon width affects dependent entities(?).
I'm assuming the dome surface is a Boundary Blend between two
First Direction curves. Expand the Constraints tab, verify
the Ribbon is being used as Tangent reference and play with
the Stretch Value for the appropriate Chain (usually a value
between 1 & 2).


(I'm pretty sure there are some helmet models floating around
on the forum. Might have provide and idea or two.)